1. The Field of the Invention
The present invention is related generally to optical signal transmission. More specifically, the present invention relates to an optical transmission component comprising a laser, a photodetector, and a laser driver within a common optical package.
2. Related Technology
High-speed communication networks have become of increased importance as the need to transmit large amounts of data continues to rise. Networks employing fiber optic technology are known as optical communications networks, and are typically characterized by high bandwidth and reliable, high-speed data transmission. Many business and governmental entities rely on high-speed communication networks in their day to day operations. As a result, fiber optic technology is increasingly employed in the transmission of data over communications networks.
To communicate over a network using fiber optic technology, fiber optic components such as fiber optic transceivers are used to send and receive optical data. Generally, a fiber optic transceiver can include one or more optical subassemblies (“OSA”) such as a transmitter optical subassembly (“TOSA”) for sending optical signals, and a receiver optical subassembly (“ROSA”) for receiving optical signals. More particularly, the TOSA receives an electrical data signal and converts the electrical data signal into an optical data signal for transmission onto an optical network. The ROSA receives an optical data signal from the optical network and converts the received optical data signal to an electrical data signal for further use and/or processing. Both the ROSA and the TOSA include specific optical components for performing such functions.
In particular, a typical TOSA includes an optical transmitter, such as a laser, for sending an optical signal. Many different types of lasers are known to those skilled in the art. One type of laser referred to as a vertical cavity surface emitting laser (“VCSEL”) emits light in a single direction through an upper surface of the laser structure. One common datacom-grade laser diode package for the transmitter is the so-called TO-Can. The TO-Can package comes in a variety of sizes and configurations.
The TOSA may further include a monitor, such as a photodiode, that generates feedback concerning performance parameters of the laser. In certain applications, the laser (e.g., a VCSEL) emission must be monitored to determine whether the power of the emitted light exceeds certain predetermined threshold magnitudes. The monitoring function may be used to avoid any possible danger from OZ the emission of unacceptably high power levels from the laser. The monitoring function may also be necessary in order to maintain required modulation rates and on/off extinction ratios.
Average power techniques may be used to control the power output of the laser. For example, an automatic power-control (APC) feedback loop may be incorporated to maintain a constant average optical output power from the laser over temperature and lifetime. Photodetectors such as, for example, photodiodes, phototransistors, or any other photosensitive component can be used to implement the monitoring function.
A TOSA also typically includes a connection for an external laser driver, which is used to control the operation of the laser. Typically, laser driver circuitry (e.g., for driving a VCSEL) is placed on an external substrate, such as a printed circuit board. However, locating the laser driver circuitry some distance from the corresponding laser can be problematic. For example, signals from the laser driver must travel through traces on the motherboard, electrical interface contacts, leads on the network package, and finally to the laser inside the package potentially causing degradation of the signal and electrical parasitics.
The laser driver circuitry is often designed to compensate for signal degradation and parasitics using methods such as peaking on electrical signals, or use of passive electrical matching networks. Control over electrical parasitics, such as parasitical capacitance, inductance, and resistance, become of increased importance to controlling laser behavior as the data transmission rates increase. That is, at increased data transfer rates smaller parasitics more adversely affect data transmission.
As a result, manufacturers typically rely on after market circuitry and consumers to compensate for degradation, and thus, to optimize performance of the optical transmission component. Removing the need to rely on consumers and external compensation circuitry would enable the manufacturer to more closely tailor the components of the laser driver to accurately compensate for parasitics and signal degradation, and thereby produce a more reliable optical transmission component.
In addition to improving signal quality by reducing signal degradation, it would also be advantageous to be able to more accurately control output characteristics of the laser (e.g. a VCSEL) by controlling operational parameters based on the temperature of the laser. Typically, temperature compensation of a VCSEL is achieved using heat transfer analysis to estimate the heat conduction of the VCSEL and heat transferred from the PC Board up the leads into the package (e.g., a TO-Can package) containing the VCSEL taking into consideration conduction and convection characteristics of the package. Miscalculation of the heat transfer of one or more components can result in overheating of the package potentially damaging the VCSEL, or potentially causing transmission degradation of the data signal transmitted by the VCSEL due to improper temperature compensation.
Some optical packages have used a semiconductor device with a laser and a photodetector in a common housing. Accordingly, this arrangement allows the photodetector to monitor the light intensity emitted by the laser. The laser and photodetector may be produced monolithically or assembled on a common structure, such as a substrate or header, to improve the accuracy of positioning of the various components. This structure can be disposed within a common package having a window through which the emitted light passes. However, existing packages still rely on external laser drivers to power the laser; and estimate laser temperature using heat transfer calculations as discussed above.
Therefore, for the reasons stated above, as well as others, it would be advantageous for an optical transmission component to include a laser, a monitor photodetector, and a laser driver within a common package. It would also be advantageous to use active internal temperature measurement within the common package to provide feedback for controlling output characteristics of the laser.